This invention relates in general to cathode sputtering devices and in particular to a new and useful apparatus for coating materials includes a cathode of generally cylindrical shape having an opened end with a holder for the material to be sputtered positioned in the opened end and including a magnet system disposed so as to influence the formation of at least two sputtering zones which may be proportionally adjusted.
The present invention relates to cathode sputtering, particularly such intended for utilizing semiconductor discs. Semiconductor discs employed for this purpose undergo a preliminary treatment in which a geometric surface structure with recesses for electrical connections is produced in an insulating layer on their surface in photolighographic processes. While the disc has typically a diameter between 50 mm and 200 mm and a thickness of some 10ths of a millimeter, the recesses have a width of mostly only a few micrometers (microns) and a depth corresponding to about the thickness of the insulating layer. A subsequent application of a metal layer (thickness of about 1 micrometer) provides contact to the discs through the recesses and still other structures are etched in the metal layer during the subsequent operations. Suitable materials for the metal layer are aluminum, aluminum alloys, titanium-tungsten alloys, etc. With cathode sputtering apparatus normally employed for metallization, namely such comprising a planar magnetron, the following arrangements are distinguished:
1. Drum-Type Apparatus:
A plurality of substrate discs is secured to the outer surface of a drum having a polygonal section. At the side of the drum, at least one sputtering magnetron is provided representing, in its region opposing the substrate disc, a substantially linear source of material including two straight line sources which are arcuately connected to each other at their ends. The erosion zone of such sources thus forms a closed path. With the drum uniformly turning about its axis, the substrate discs are uniformly coated, in the axial direction due to the line source and in the peripheral direction due to the uniform rotation. The spacing between the substrate in coating position and the parallel magnetron can be varied within certain limits, without thereby exceeding the permissible tolerances for the uniformity of the layer thickness.
2. Dish-Type Apparatus:
In this arrangement, a plurality of substrate discs is placed on a large circular rotary dish. At least one magnetron is provided thereabove. The erosion zone of this magnetron in the region opposite to the substrate discs should be shaped to coat the substrates uniformly during a uniform rotation of the dish. In this prior art arrangement again, the spacing between the substrates and the planar magnetron can be varied within certain limits without thereby exceeding the tolerances of the uniformity of the layer thickness.
3. Single-Disc Apparatus
In this apparatus, a single round substrate disc is placed in fixed position opposite a planar magnetron having is erosion zone in the form of a ring. A certain relation between the substrate disc diameter, the diameter of the erosion zone circle, and the spacing of the substrate from the magnetron must be maintained in this instance, to meet distribution tolerances of .+-.5% or less. With a too small spacing, the substrate would become coated in an annular zone opposite to the erosion zone with a thicker layer than at the center. With a large spacing, on the contrary, the coating of the substrate would become thickest at the center, and thoroughly taper out to the circumference.
Aside from the uniformity of the layer thickness, a best possible satisfactory coating of any steps of the substrate surfaces to be coated, such as at the edges of the mentioned recesses for electrical contacting, should be obtained in any case, with regard to both the local distribution of the substrates and to the orientation of the edges. The coating attainable with prior art arrangements of surfaces extending perpendicularly to a substrate surface, the so called "step coating" (indicated usually in percent of the layer thickness at a certain distance from the step) and uniformity thereof, have frequently been unsatisfactory. An unsatisfactory step coating is often obtained in a single-disc apparatus close to the edge of the substrate disc on the step surface facing the outside. But in drum and dish type apparatus also, the value of step coating of vertical steps hardly exceeds 50%. This is caused by the directional distribution of the sputtered cathode material. This distribution follows Lambert's cosine emmision law, i.e. its maximum intensity perpendicular to the plane of the cathode. Basically, this does not change if an erosion trench is formed during the material removal from the sputtered surface of the magnetron.
Occasionally, a modification of the planar magnetron with a plasma ring on a conical cathode surface has been used for single-disc apparatus. An obliquely inwardly directed material stream is thereby obtained. The step coating on the substrate discs, however, is only insignificantly improved with this prior art measure.